For a high speed transmission connector, particularly for a connector or a cable located on a transmission path of a differential signal, a characteristic impedance matching is required, in addition to the requirement for a simple and easy inter-connection of the existing apparatus.
For example, in a connector for communication in an audio/visual apparatus, reduction of the number of connectors to be connected and miniaturization of the connector per se have been continuously required, and in addition, the following problem has arisen as a new requirement for the connector in line with the new high speed digital transmission. That is, when there is an impedance mismatch in the connector portion, a signal of an image or sound is deformed or reflection occurs, and, as a result, the image or sound cannot be properly reproduced. Therefore, in such a connector to be inserted into a high frequency signal transmission path, the matching performance of the impedance is also one of the important requirements.
Japanese Patent Laid-Open Publication No. Hei 7-106027 discloses a technology considering characteristic impedance of a connector. In this technology, a high frequency signal transmission path is realized by a contact having a non-coaxial structure and constructing a control signal transfer path by also the same contact parts whereby the low cost and the miniaturization may be attained.
In a recent signal transmission connector, the outside of a housing where contacts are arranged is covered with the metal shell. This is because, by covering the housing with the metal shell, the noise or loss due to the generation of an electromagnetic wave radiation may be effectively prevented.
In the case where this kind of connectors is a pair of connectors (composed of a male connector and a female connector) to be coupled with each other, metal shells are provided, as an electromagnetic shield, for the respective connectors. At the time of coupling, generally, the metal shell on one connector is inserted into the metal shell on the other connector so that the metal shells are electrically connected to each other, thereby to place it in a mode where these potentials are maintained at an equal level and the grounding is to be made.
The metal shells of the two connectors are formed into a sleeve-shape having an engaging portion for coupling with each other. Therefore, since the metal shell of one connector is inserted into the metal shell of the other connector, the metal shell and the connector placed therein are inevitably most closed to each other. As a result, there arises a problem of mismatch in impedance at the engaging portion.
In this respect, some conventional connectors adopted a method of adjusting the characteristic impedance on the basis of a pitch of the contacts, the width dimension of the contacts, or on the basis of an induction rate of an insulator (housing) for holding the contacts.
However, with these methods, there are various drawbacks in designing and manufacturing the connectors, in that, for adjusting the characteristic impedance, the connector itself or its pitch is widened, thereby sacrificing the miniaturization and high density aspects of the connector. In addition, for the contacts to be made of a plate material, it must be selected from materials having a thickness which is not generally available on the market.